This glossary defines 26 terms you will meet when working on visibility in AI search, from AEO and AI Overviews to llms.txt, query fan-out and zero-click search. Each entry opens with a one-sentence definition you can quote, followed by why it matters in practice. Terms are listed alphabetically and link to each other where they are related. For how the pieces fit together, read our complete guide to generative engine optimization.
AEO (Answer Engine Optimization)
Answer engine optimization is the practice of structuring content so that search features and assistants can use it as the direct answer to a question, for example in featured snippets, voice answers and AI Overviews. It favors concise answers placed right under a question heading. AEO overlaps heavily with Geo; the main difference is that GEO also covers assistants that write longer answers from several sources.
AI Crawler
An AI crawler is an automated bot that fetches web pages for an AI company, either to train models, to retrieve pages for live answers or to fetch a page a user asked about. Examples include OpenAI's GPTBot (training), OAI-SearchBot (search) and ChatGPT-User (user requests), and PerplexityBot. Each can be allowed or blocked separately in robots.txt.
AI Mode
AI Mode is Google's conversational search experience, which answers a question with an AI written response and supporting links, and lets the user ask follow-up questions. Google describes it as using a query fan-out technique, running many related searches for one question. Google documents how sites appear in it in its AI features guidance.
AI Overviews
AI Overviews are AI generated summaries that Google Search shows above or among the regular results for some queries, with links to the pages used as sources. There is no special markup for inclusion: Google says the same SEO best practices apply, and a page must be indexed and eligible to appear with a snippet.
AI Visibility
AI visibility is how often, how prominently and how accurately a brand appears in answers from AI assistants and AI search features for the questions its buyers ask. It is usually measured with a fixed set of prompts, tracking mention rate, citation rate and share of voice. See our guide to AI visibility checkers.
Citation Rate
Citation rate is the share of tracked prompts for which an AI answer links to one of your pages as a source. A brand can be mentioned without being cited, and cited without being recommended, so citation rate is tracked alongside mention rate.
E-E-A-T
E-E-A-T stands for experience, expertise, authoritativeness and trustworthiness, the qualities Google's search quality rater guidelines use to judge whether content is reliable. It is not a single ranking signal. On a page it shows through named authors with real credentials, first-hand experience, cited sources and accurate, current facts.
Entity
An entity is a distinct, identifiable thing, such as a company, product, person or place, that search engines and language models can recognize and connect to facts about it. Consistent names and facts, structured data and sameAs links help engines resolve your brand to the right entity rather than confusing it with a similarly named one.
FAQPage Schema
FAQPage schema is Schema.org structured data that marks up a list of questions and their answers on a page. Since August 2023, Google shows FAQ rich results only for a limited set of well-known government and health sites, but the markup still states question and answer pairs in a form machines read reliably. Only mark up questions that are visible on the page.
Generative Engine
A generative engine is a search or assistant product that writes an answer to a query in natural language, usually drawing on retrieved web pages, instead of only returning a list of links. ChatGPT search, Perplexity, Gemini, Claude, Microsoft Copilot, Google AI Overviews and AI Mode are all generative engines.
GEO (Generative Engine Optimization)
Generative engine optimization is the practice of making a website easy for AI answer engines to find, understand, trust and cite, so that a brand is named and linked inside AI written answers. The term comes from a 2023 research paper presented at KDD 2024. Read our complete guide to GEO.
Grounding
Grounding is the process of tying an AI model's answer to specific source material, such as retrieved web pages or documents, so the answer reflects those sources rather than only the model's training data. Grounded answers are less prone to hallucination and can cite the sources they used.
Hallucination
A hallucination is a statement an AI model presents as fact that is false or not supported by any source. For brands, common hallucinations are wrong prices, discontinued products or features a company never offered. Clear, consistent facts on your own site reduce the risk.
IndexNow
IndexNow is an open protocol that lets a website notify participating search engines, including Bing, the moment a URL is added, updated or deleted. It speeds up discovery of changes compared with waiting for a crawl. The protocol is documented at indexnow.org.
JSON-LD
JSON-LD (JavaScript Object Notation for Linked Data) is the format Google recommends for adding Schema.org structured data to a page, placed in a script tag separate from the visible content. Because each item can carry an @id, JSON-LD can link entities across a site, for example connecting an article to its author and the author to their employer.
Knowledge Graph
A knowledge graph is a database of entities and the relationships between them, such as Google's Knowledge Graph, which search engines use to understand and display facts about people, companies and things. Being well represented in knowledge graphs helps AI systems describe your brand consistently.
llms.txt
llms.txt is a proposed standard file, placed at the root of a website, that gives language models a short Markdown guide to the site and links to its most important pages. It was proposed in 2024 and is described at llmstxt.org. No major engine requires it, but it is cheap to add. You can read ours.
Mention Rate
Mention rate is the share of tracked prompts for which an AI answer names your brand, whether or not it links to your site. It is the broadest measure of AI visibility, and is usually compared with competitors as share of voice.
Prompt Tracking
Prompt tracking is the practice of running a fixed set of buyer questions through AI assistants on a regular schedule and recording which brands and sources each answer mentions. Because AI answers vary between runs, prompt tracking looks at trends over weeks rather than single results.
Query Fan-Out
Query fan-out is a technique in which an AI search system breaks one question into many related sub-queries, searches for each and combines the results into one answer. It means a page can be retrieved for a sub-question the user never typed, which rewards pages that answer specific questions clearly.
RAG (Retrieval-Augmented Generation)
Retrieval-augmented generation is a method in which an AI system first retrieves relevant documents or web pages and then generates its answer from them. Most AI search products use some form of RAG, which is why a page must be crawlable and indexed before it can be cited.
robots.txt
robots.txt is a plain text file at the root of a website that tells crawlers which parts of the site they may fetch, with separate rules for each user agent. It is the main way to allow or block specific AI crawlers. Note that a CDN or firewall can still block a bot that robots.txt allows.
sameAs
sameAs is a Schema.org property that lists URLs of official profiles or reference pages describing the same entity, such as a company's LinkedIn page or a person's professional profile. It helps search engines and language models confirm that the entity on your site is the same one described elsewhere.
Share of Voice (AI)
AI share of voice is your brand's share of all brand mentions across a set of tracked prompts, compared with competitors named in the same answers. It shows whether you are gaining or losing ground in AI answers even when the total number of mentions changes.
Structured Data
Structured data is code added to a page, usually Json-ld using the Schema.org vocabulary, that describes the page's content and entities in a standard, machine-readable form. Common types include Organization, Product, Article, Person, BreadcrumbList and FAQPage. Google explains the basics in its structured data introduction.
Zero-Click Search
A zero-click search is a search in which the user gets the answer on the results page or in an AI answer and does not click through to any website. AI Overviews and assistants increase zero-click behavior, which is why being named and cited inside the answer matters as much as ranking.
